Depressed teens with anhedonia, or the inability to experience pleasure, have lower levels of the neurotransmitter GABA in a key mood-regulating region of the brain, according to an NIMH-funded study published online October 3, in the Archives of General Psychiatry. The researchers note that focusing on specific symptoms and using different types of measures may offer new clues to the pathways and processes underlying depression and other mental disorders.

Background

Symptoms of depression in teens can be highly varied and tend to overlap with signs of other disorders. Because of this, adolescent depression can be hard to study using conventional research tools and methods.

Guided by findings in adults, Vilma Gabbay, M.D., of New York University School of Medicine, and colleagues decided to focus on the neurotransmitter GABA. GABA has many important roles throughout the body and is involved in regulating communication between brain cells. Abnormalities in GABA production or function in the brain have been linked to several mental disorders, including schizophrenia and postpartum depression, and possibly learning disorders. GABA has also been linked to anhedonia, a symptom present in up to 59 percent of depressed teens.

The researchers used a type of specialized MRI to measure GABA levels in the brain region known as the anterior cingulate cortex (ACC) in 20 teens with depression, half of whom also had anhedonia. They were compared to 21 matched controls who did not have depression or anhedonia. Levels of anhedonia were scored numerically according to clinician- and self-rated assessments.

Results of the Study

Compared to controls, teens with depression and anhedonia had significantly lower ACC GABA levels. Lower ACC GABA levels were associated with more severe anhedonia symptoms among all participants.

Significance

The findings support a role for GABA in anhedonia and depression among teens. Also, by correlating GABA levels with numeric measures of anhedonia severity, the researchers were able to assess participants’ symptoms along a continuum. Compared to traditional measures that categorize symptoms only as being either present or absent, such continuous or “dimensional” measurements may provide greater specificity to disease evaluations in research.

What’s Next

Additional studies in larger populations are needed to confirm these findings. Advances in imaging techniques and technology may help to identify differing roles for other neurotransmitters associated with depression.